The present invention relates generally to drive mechanisms for bicycles of all types, including stationary exercise bicycles, and any other devices or machinery, whether manually or otherwise driven. More particularly, the present invention relates to a pedal operated drive mechanism which facilitates a more efficient transmission of force than conventional drive mechanisms.
The operation of bicycles and other pedal operated vehicles or devices are typically propelled by a conventional drive mechanism which employs a drive sprocket, a gear and a drive chain operatively associated with the drive sprocket and gear to transmit the manual force applied to a set of pedals connected to the drive sprocket, thus enabling the bicycle or other vehicle to move, or to otherwise power a device, by overcoming frictional or other resistive forces. Conventional drive mechanisms are manifest in other forms, though most such conventional drive mechanisms share the same disadvantages, including inefficient transmission of the manual force and/or the inefficient production of such manual force. With respect to the latter, the typical drive mechanism on a bicycle or other similarly operated vehicle provides for a pedal path which is circular, tracking the crank circle. The result is a pedal system which has a power stroke which is equal to or shorter than the return stroke. Moreover, as opposing pedal cranks are displaced from one another by 180.degree., every 360.degree. rotation of the drive sprocket includes two "dead spots" at which the pedal cranks are simultaneously in the vertical position. As can be appreciated, no productive force can be applied to the pedals when the pedal cranks are in such vertical positions. In addition to generally providing an inefficient path of movement for the pedals, the typical drive mechanism permits the production of only a limited degree of torque and/or power as the sizes of the pedal crank, drive sprocket and other components must be limited to accommodate design specifications. For instance, on a bicycle, it is desirable to position the seat of a bicycle as close to the ground as possible given the height of the individual for whom the bicycle is designed. Thus, as the drive sprocket is located substantially directly beneath the seat, the length of such persons legs require that the drive sprocket be even closer to the ground. As a consequence, the length of the pedal crank must be limited so that the ground does not interfere with the movement of the pedals at the bottom of the power stroke.
The above disadvantages and shortcomings have been broadly recognized by those in the bicycle and related industries, and attempts have been made to alleviate the same. For instance, U.S. Pat. No. 2,184,049 to Lienhard discloses a pedal drive for a bicycle which provides a return stroke which is shorter than the power stroke. However, this is only accomplished by the use of a dual sprocket drive system arranged in conjunction with a complicated array of levers and cranks. Thus, each drive sprocket includes a crank, or more particularly a driving crank and a pedal crank. A pedal lever, which includes a pedal at one end, is connected to the pedal crank of the first sprocket. The pedal lever is connected to the driving crank of the second sprocket by means of a link. All points of connection are rotatable so that when the drive mechanism is put into operation, the driving crank, pedal crank, pedal lever and link move in various directions with respect to one another. This drive mechanism is further complicated by providing means to vary the power stroke, even while riding, by moving the pedal relative to the driving crank on the second sprocket.
Further, a bicycle pedal drive mechanism intended to increase torque is disclosed in U.S. Pat. No. 4,872,695 to Silvano et al. The pedal crank of a conventional drive mechanism is extended, at the end of which an elongate bar is pivotally connected thereto. The elongate bar has an elongate back end which extends rearwardly to a point adjacent to the axis of the rear wheel of the bicycle, where it is slideably disposed in a sleeve. The elongate bar also includes a front end which is disposed at an obtuse angle to the back end of the elongate bar, and includes a pedal at the end thereof. It is the link of the front end which provides the increase in transmitted torque. The angle of the front of the elongate bar is provided to prevent the pedal from striking the ground when the pedal is at the bottom portion of the power stroke. The back end of the elongate bar, and slideable disposition thereof, is provided simply because the front end must be pivotally attached to the crank, and without the back end of the elongate bar, the front end would always be in the vertical position. If the crank were simply extended, the same torque advantage might be realized, but the entire drive mechanism and the seat of the bicycle would have to be raised further above the surface of the ground to prevent pedals from striking the ground before beginning the return stroke.
The Lienhard and Silvano et al patents do not, however, adequately address the above described shortcomings, nor do they provide all of the desirable features of an improved drive mechanism. Those in the art will recognize that Lienhard undesirably provides a complicated linkage as well as an additional drive sprocket to provide a pedal path in which the return stroke is only modestly shorter than the power stroke. Silvano et al does not address the disadvantage of having dead spots in the pedal path, nor in providing a power stroke which is adequately or substantially longer than the return stroke in order to increase the efficiency thereof. Further, Silvano et al employs an elongate bar which is in reciprocating sliding relationship with a support at the rear of the bicycle. The movement of the elongate bar is not desirable for safety reasons, and the sliding relationship is undesirable for maintenance purposes.
It is apparent from the foregoing that a simply structured drive mechanism which alleviates the inefficiencies associated with conventional drive mechanisms is warranted. The present invention thus addresses the above and other shortcomings which heretofore were lacking with respect to drive mechanisms for bicycles and other vehicles or other devices